1. Field of the Invention
This invention relates to an automotive suspension control system and method for operating an adjustable suspension unit when a vehicle equipped with the suspension unit is operated over an undulating road surface.
2. Disclosure Information
Automotive suspensions employing adjustable suspension units typically utilize one or more sensors for detecting the position of one or more portions of the suspension with respect to either another part of the suspension itself or another part of the chassis of the vehicle. Such a sensor is disclosed in U.S. patent application Ser. No. 07/126,082, filed concurrently herewith. In the case of vehicles using load leveling or air or hydropneumatic suspension systems, it is necessary to know the ride height of the vehicle in order to determine whether correction of the ride height is required. In the event, for example, that the ride height is less than prescribed limits, as determined by a height sensor, an adjustable suspension unit may be given the command to increase the ride height. Conversely, in the event that the ride height exceeds the prescribed limits, the adjustable suspension unit may be given the command to lower, or decrease, the ride height.
In one embodiment, the present invention proposes to use a unitary suspension motion sensor not only in conjunction with a ride height adjusting system but also as a suspension velocity transducer for use with an adjustable suspension damper. A control system and method are proposed for operating suspension dampers according to the sensed and calculated speed of the suspension's movement in jounce or rebound.
Suspension designers have utilized a variety of control algorithms for operating the damping feature of adjustable suspension units as a function of various operating parameters. U.S. Pat. No. 3,807,678 discloses a system in which damping is controlled as a function of body velocity which is derived from integration of an accelerometer output. The '678 patent suggests that a displacement transducer might be employed between the controlled mass and its support to monitor parameters such as relative velocity, but does not disclose any manner in which this could be done.
U.S. Pat. No. 4,065,154 discloses a suspension damper and control system in which damping is controlled both as a function of the pressure developed within the damper and the vertical velocity of the suspension and associated road wheel with respect to the body. The time response characteristics of this system may suffer because of the time lag between changes in suspension vertical velocity and changes in pressure within the shock absorber. A system according to the present invention, however, need not use suspension unit pressure as a control variable, and as a result the time response characteristics of such system should be superior to those of the '154 patent.
U.S. Pat. No. 4,647,068 discloses a system in which rear wheel damping is controlled as a function of measured front wheel ride height. In this case, the movement of the front wheels is detected by a sensing mechanism and the resulting information is used in a control scheme for adjusting the rear damping. This system suffers from lack of ability to control the damping of the front wheels in response to the bumps encountered by the wheels.
U.S. Pat. No. 4,579,366 discloses a system in which the damping force capability of a hydropneumatic suspension is controlled as a function of wheel vertical location and velocity. Because a control system according to the present invention will utilize wheel position as a control input only when not only suspension unit damping, but also suspension unit ride height are being controlled, the present invention may be practiced in certain cases by means of a sensor which produces a signal representative of only road wheel vertical velocity and not vertical velocity and position.
U.S. Pat. No. 4,589,676 discloses an automotive suspension control system in which the frequency and maximum amplitude of the suspension's vertical oscillations are measured and the damping adjusted accordingly. This system could be expected to provide less than optimal time response characteristics because of the asserted need to evaluate the operation of the suspension over several cycles before making a decision on the damping level to be used.
U.S. Pat. Nos. 4,616,848 and 4,674,767 disclose systems in which remote sensing is used to detect road roughness which then is compensated for by changing the damping of adjustable suspension units. These systems are disadvantageous insofar as they require an additional transducer and supporting electronics.
It is an object of the present invention to provide a control system for an adjustable automotive suspension unit which will preferentially adjust the suspension unit in the event that a vehicle with this system is driven over a road surface tending to induce an undulating vertical motion in the vehicle. If the adjustable suspension unit is moved from a "normal" to a "firm" setting in this situation, excessive undulation will be averted. Because the suspension unit is adjusted preferentially according to certain threshold criteria, the suspension unit will be adjusted only when such adjustment is warranted; adjustment will not normally be made on road surfaces such as gravel where adjustment to a firmer setting would cause a deterioration of ride quality.
It is an advantage of the present invention that a control system according to this invention has the capability of responding to a single road surface input. Thus, a system according to this invention need not encounter a series of road surface inputs before making a decision to adjust the suspension units.
It is a further advantage of the present invention that a system according to this invention will economically produce, by means of a single sensor unit, not only suspension position information but also suspension velocity information without the necessity of an accelerometer.
It is a still further advantage of the present invention that a system according to this invention is simpler than one which would employ accelerometers to determine suspension velocity.
Other objects, features, and advantages of the present invention will become apparent to the reader.